This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In hyperoxic contrast studies modulated by the blood oxygenation level-dependent (BOLD) effect, it is often that hyperoxia is a purely intravascular, positive contrast agent in T2*-weighted images, and the effects that are not due to BOLD contrast are small enough to be ignored. In this project, we reevaluated this assumption, with the goal of characterizing non-BOLD effects in T2*-weighted hyperoxic contrast studies. The quality of oxygen as an intravascular contrast agent depends not only on its minimal effects on the underlying physiology, but also on its minimal relaxation effects not due to the dilution of deoxyhemoglobin. Although it is known that molecular oxygen dissolved in the blood has a relatively weak T2 and T1 relaxivities molecular oxygen has been shown to be effective as a T1 contrast agent in body fluids, with a fast wash-in of a significant concentration of molecular oxygen into these tissues. Another important effect is the disruption of the static magnetic field (B0) in the frontal lobes of the brain due to the influence of paramagnetic gaseous oxygen in the upper airway, which has not yet been characterized in hyperoxic contrast studies of the human brain.